The present invention relates to an electrically conductive adhesive and a method for connecting a circuit member having a plurality of conductive terminals to a substrate including a mounting surface having a plurality of spaced conductive paths utilizing the adhesive.
In many electrical applications, it is desirable to connect an electrical component having a plurality of conductive terminals to a substrate including a plurality of laterally spaced conductive paths such that the conductive terminals are aligned with the conductive paths in a predetermined pattern. For proper function, current is passed from the aligned conductive terminals to the substrate path, or visa a versa. The desired function is referred to as uniaxial conductivity. It is undesirable for current to pass between laterally spaced terminals or conductive pads, such conductivity causing shorting of the circuit.
Conventional methods of connecting conductive terminals to a substrate, for example, a PCB, include soldering techniques. As the soldering temperature is high, up to about 300.degree. C., soldering requires specific temperature resistant components and substrates. Soldering further requires precise dot deposition; that is, application of the solder only on the terminals and not therebetween, to avoid possible shorting of circuits. Therefore, conventional soldering technique requires a number of further treatments to assure the electrical connection between the components and the substrate. This will inevitably increase the manufacturing cost thereof.
U.S. Pat. No. 4,820,376 issued to Lambert discloses a method of fabricating a layer of silicone elastomer material including chains of electrically conducting particles extending essentially perpendicular to the major surfaces of the layer. The method includes the step of removing a portion of at least one of the major surfaces by plasma etching so that the particles at the ends of the chains protrude through the etched surface. However, in the application of the silicone elastomer materials, electrical connection is achieved only when the two protruded ends of the chains are compressed. Further, as the conducting particles chains are randomly distributed in the elastomer, and are not fixed at specific positions, the application of the silicon elastomer layer is thus limited.
U.S. Pat. Nos. 4,667,401, 4,720,740 and 4,868,637 issued to Clements, disclose a method of connecting a circuit member having a plurality of laterally spaced conductive terminals to a substrate including a mounting surface having a plurality of laterally spaced conductive paths. This method includes applying an adhesive including a resin having a viscosity of 10,000 to 440,000 cps and having a 20 to 25 percent by weight content of conductive metal particles suspended therein over the mounting surface; mounting the circuit member on the adhesive while vertically aligning the conductive terminals over preselected ones of the conductive paths; applying pressure against the terminals and the conductive paths to concentrate the percent by weight content of the conductive metal particles to between 40 to 50 percent by weight; and hardening the adhesive under pressure. However, to concentrate the conductive metal particles merely by applying pressure can not guarantee high success rates of electrical connections. And, as the thermal expansivity of the metal conductive terminals is different from that of the adhesives, nonconnection often occurs due to poor contact between the conductive terminals and the adhesives when the surrounding temperature is high.